<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>变量</title>
</head>
<body>
    <script>
        console.log(isNaN(NaN));    // true
        console.log(isNaN('123'));  // false
        console.log(isNaN('hello'));// true
        console.log(isNaN(true));  // false
        </script>
</body>
</html>